This invention relates to interactive displays, that is, to devices that display data and also allow an operator to input fresh data or change the data that is displayed.
When the amount of data is small, one method of displaying it has been to use illuminated press switches Each switch will in general be labelled and can be regarded as displaying the value of a particular bit whose significance is indicated by the labelling.
When the amount of information is large it has been common to display it on a cathode-ray screen. In this case the information will be conveyed by the pattern of the lit areas--they may, for example form letters of the alphabet or graphic designs. Interactive input can be by a separate keyboard or, by a "light pen" which detects light from the screen and can be used to draw designs on it. It has also been proposed to use light pens with display devices using inherent-memory gas-plasma display cells or light-emitting diodes. In the devices, too, the display conveys information by the pattern assumed by the lit elements.